The present invention relates to a damping valve for pressure medium-actuated operating circuits and to the use of such a damping valve in a power steering system for motor vehicles. In the damping valve, a flow passage cross-section is regulated by the interaction of housing, spring element, cover, and counter-contour.
In hydraulically or pneumatically actuated operating circuits, vibrations may arise which originate, for example, in the servo pump or due to impacts from a user. In power steering systems such vibrations can be generated, for example, by shocks introduced by the roadway into the steered wheels of the vehicle or into the power steering system.
French Published Patent Application No. 2 632 371 describes a damping valve which separates two pressure chambers from one another and influences the volume flow path between the two pressure chambers in a controlled manner. The damping valve has an elastic valve plate which is normally in a neutral position and, when a pressure difference arises between the two chambers, is displaced from its neutral position toward the lower pressure. A disadvantage of these damping valves is the large number of component parts and the associated large space required for installation. Another disadvantage is the fact that these nonreturn valves operate in only one direction and the damping characteristics of these valves can be influenced only to a very limited extent. French Published Patent Application No. 1 535 025 describes a damping valve for pressure medium actuated circuits having a housing and a flow-through channel between two pressure medium connections. German Published Patent Application No. 196 03 183 describes a power steering system for a motor vehicle in which damping valves are arranged in the operating lines between a control valve and the working chambers of a servo motor.
It is therefore an object of the present invention to provide a damping valve having a simple design which is versatile in its application, operates in both directions and can exhibit different damping characteristics.
The above and other beneficial objects of the present invention are achieved by providing a damping valve in which a spring element is exposed to pressure or by the flow of a medium, whereby a variable cross-sectional area can be obtained which produces the desired damping effect through variable throttle geometries, depending on the configuration. The same or different damping characteristics may be achieved in the two directions of flow.
The damping valve can be represented very simply by the interaction of a spring element and a counter-contour. The spring element is designed preferably in the form of a circular disk which can be displaced axially within a housing. Further variants include spring elements in the form of polygons or curves. The characteristics of the damping valve can be modified by variations in the spring element, the cross-section, and the counter-contour.
In order to modify the flow passage cross-section, the outer and/or inner contour of the spring element is designed so that it can move axially in relation to the contour of the housing. Along its axial extension, the contour of the housing has different cross-sections, through which the damping characteristics can be influenced.
The mobility of the outer and/or inner contour of the spring element can be achieved due to the fact that the spring element is centrally supported on the housing or on the counter-contour, and is made of an elastic material. The movable contour of such a spring element can be adjusted in an axial direction as a function of the pressure and flow conditions in the damping valve.
A damping action can be produced even for the smallest movements by pre-stressing the spring element in a controlled manner. This allows pressure to be controlled even in the case of a flat counter-contour, by the axial positioning of the spring element and variable opening cross-sections.
By specifying a free opening, for example through a bent spring element, a permanent flow can also be implemented, which allows the damping action to begin only at higher flow rates.
In the case of power steering systems of motor vehicles, undesirable vibration and noise effects, for example, can thus be suppressed.
In its simplest form, the damping valve may be manufactured as a compact unit having three parts, forming the basis for adjustable damping valves having a wide range of damping characteristics.
The free choice of housing, counter-contour and spring element even permits the creation of damping functions, i.e., the damping characteristics can be varied as a function of different parameters.
If a flow passage cross-section of the damping valve at its neutral setting is selected that is large enough to allow unimpeded passage up to a certain volume flow rate, the overall size of the damping valve can be kept small. In addition, this permits a design which is particularly insensitive to the flow rate, and thus also insensitive to noise.
There are many ways of configuring the characteristics of the damping valve. For instance, the pressure level can be raised or lowered using the adjusting screw. The increase of the slope of the pressure/volume flow curve can be modified by selection of the fit between damping element and housing.
The timing of the beginning of the damping effect can be influenced by varying the rigidity of the damping element, e.g., through the selection of the thickness of the damping element.
The use of such damping valves in power steering systems of motor vehicles is particularly advantageous, since in this case a very limited installation space is available and different types of vibration can occur, with noise effects and negative effects on the steering response which can be individually eliminated through the variability of the damping valve.